Micromachined apparatus for improved reflection of light

ABSTRACT

A micromachined apparatus for reflecting light is described that is designed to reduce losses in quality or intensity of light. Mirrors are used having lengths that are longer than their widths to reduce clipping of light when a mirror is located at an angle with respect to light falling thereon. Relatively long mirror torsion components are used to reduce forces required to pivot the mirrors. Regardless of the dimensions of the mirrors and the use of long torsion components, the mirrors are still located relatively close to one another. The relatively close positioning of the mirrors is due to a combined use of notches formed in support frames to which the torsion components are secured, oval shapes of the mirrors which take up less space than rectangular shapes, matching oval openings in the support frames, and the arrangement of the support frames in a non-rectangular array wherein tips of the support frames are located between one another.

FIELD OF THE INVENTION

The invention relates to a micromachined apparatus for reflecting light.

BACKGROUND OF THE INVENTION

Optical fibers are commonly used in networks such as the Internet.Optical fibers are often bundled together in an array, each carryingdifferent signals of light. In certain instances the signals of lightcarried by the different optical fibers have to be switched into adifferent arrangement. The optical fibers are provided as input fibersinto an optical switch and further optical fibers are provided as outputfibers from the optical switch. A micromachined apparatus for reflectinglight from the input optical fibers is located in a path of light beingemitted from the input optical fibers. The micromachined apparatus forreflecting light usually has an array of mirrors which are arranged in amanner similar to the input optical fibers. Each mirror reflects lightfrom a respective input optical fiber to the output optical fibers. Eachmirror can be pivoted so that the light reflected therefrom is directedto a selected one of the output optical fibers.

Losses in quality and intensity of the light used in such a switch mayoccur. Losses may be due to the mirrors being located too far apart ordue to clipping of edges of bundles of light when the mirrors arelocated at an angle to the bundles of light. Locating the mirrors tooclose to one another may, however, require forces that are too high forpurposes of pivoting the mirrors against torsion spring forces whichtend to restore the mirrors.

SUMMARY OF THE INVENTION

A micromachined apparatus for reflecting light is provided comprising asupport structure and a plurality of mirrors. Each mirror is pivotallysecured to the support structure. A first to a third adjacent ones ofthe mirrors are located at corners of a first triangle. Each corner ofthe triangle is less than 90°.

Other features and advantages of the present invention will be apparentfrom the accompanying drawings and from the detailed description thatfollows below.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and notlimitation in the figures of the accompanying drawings, in which likereferences indicate similar elements and in which:

FIG. 1 is a plan view of a micromachined apparatus for reflecting lightaccording to an embodiment of the invention;

FIG. 2 is a cross-sectional side view on 2—2 in FIG. 1; and

FIG. 3 is a cross-sectional side view on 3—3 in FIG. 1.

DESCRIPTION

A micromachined apparatus for reflecting light is described that isdesigned to reduce losses in quality or intensity of light.“Micromachined” refers to structures fabricated by selective etching ordeposition. As described in more detail below mirrors are used havinglengths that are longer than their widths to reduce clipping of lightwhen a mirror is located at an angle with respect to light fallingthereon. Relatively long mirror torsion components are used to reduceforces required to pivot the mirrors. Regardless of the dimensions ofthe mirrors and the use of long torsion components, the mirrors arestill located relatively close to one another. The relatively closepositioning of the mirrors is due to a combined use of notches formed insupport frames to which the torsion components are secured, oval shapesof the mirrors which take up less space than rectangular shapes,matching oval openings in the support frames, and the arrangement of thesupport frames in a non-rectangular array wherein tips of the supportframes are located between one another.

FIG. 1 to FIG. 3 of the accompanying drawings illustrate a micromachinedapparatus 10 for reflecting light according to an embodiment of theinvention. The apparatus 10 includes a substrate 12, a support structure14, a plurality of support frames 16, and a plurality of mirrors 18 andmay be manufactured utilizing photographic techniques, ion etchingtechniques or any other technique as will be evident to a person skilledin the art. the support structure 14 is formed on the substrate 12 so asto be secured to the substrate 12. The support structure 14 is in theform of a honeycomb defining generally hexagonal openings. In oneimplementation, the substrate is fabricated from silicon, the supportstructure 14 is formed by a reactive ion etching of silicon, and themirrors 18 are formed by etching silicon.

Each frame 16 is formed to define an oval opening 20. Deep notches 22Aand 22B are formed in a surface of the oval opening 20. The notches 22Aand 22B are formed at 0° and 180° about the oval opening 20,respectively. Notches 24A and 24B are also formed in an outer surface ofthe frame 16. The notches 24A and 24B are located at 90° and 270° on theouter surface of the support frame 16.

The oval shape 20 has a length L1 and a width W1. The length L1 extendsbetween the notches 22A and 22B and the width W1 between the notches 24Aand 24B. The length L1 is typically about 320 microns and the width W1is about 270 microns. The oval shape 20 thus has a long axis between thenotches 22A and 22B. Because of the oval shape 20 and its orientation,and to allow for the notches 22A and 22B to be formed, the frame 16 hasa length L2 and a width W2 wherein the length L2 is much larger that thewidth W2. The frame 16 thus takes up more space along its length L2 thanalong its width W2. The length L2 is typically about 520 microns and thewidth W2 about 340 microns.

Each frame 16 is located within a respective opening in the supportstructure 14 and is secured to the support structure 14 with two frametorsion components 26. Each frame torsion component 26 has a first end28 and a second, opposing end 30. The first end 28 is non-rotationallysecured to the support structure 14. The frame torsion component 26extends from the first end 28 into a respective one of the notches 24Aor 24B, and the second end 30 is non-rotationally secured to the frame16. The frame 16 is thereby suspended above the substrate 12 by theframe torsion components 26. The frame 16 has a minimum spacing S asmeasured from directly next to the notch 24A to the support structure14. The frame torsion component 26 has a torsion length from the end 26to the end 30 which is more than the minimum spacing S.

The frame 16 can be pivoted about an axis through the frame torsioncomponents 26. The entire length of each frame torsion component 26,i.e. From its end 28 to its end 30, winds up, or twists against atorsion spring force thereof, thus tending to return the frame 16 to itsoriginal position. It can thus be seen that, although the minimumspacing S can be kept relatively small, each spring torsion component 26has a torsion length that is relatively long, in particular longer thanthe minimum spacing S. By keeping the torsion length relatively long, atorsion spring constant of each spring portion component can beincreased with a corresponding decrease in torsion required to pivot theframe 16 by a predetermined degree. The relatively long torsion lengthis allowed for due to the extra space provided by the notch 24A or 24B.Another thinner frame having less material may also provide a similaramount of space but may include too little material for purposes ofstrength. The notches 24A or 24B thus provide additional space whilemaintaining strength in the frame 16.

The frames 16 are located in a non-rectangular array. The frames 16A,16B, and 16C pivot about a common frame axis 31 and the frames 16D, 16E,and 16F pivot about a common frame axis 32 which is parallel to andspaced from the frame axis 31. A line can be constructed from a centerpoint of an oval opening 20 of one frame (e.g. 16A) to an oval opening20 of an adjacent frame (e.g. 16D). By constructing such lines betweenadjacent oval openings 20, it can be seen that center points of the ovalopenings 20 are located at corners of contiguous triangles. For example,the oval openings 20 of the frames 16A, 16B, and 16D are locatedrespectively at corners 40, 42, and 44 of one triangle. Each corner, 40,42, and 44 is less than 90°. The corners 40 and 42 are equal to oneanother. By so locating the frames 16, a zigzag pattern is createdfollowing center points of oval openings of the frames 16A, 16D, 16B,16E, 16C, and 16F.

Each oval opening 20 has a center line 46 extending along its length L1.The center line 46 of the oval opening 16D is spaced and parallel to thecenter line 46 of the oval opening 20 of the frame 16A. Similarly, thecenter line 46 of the oval opening 20 of the frame 16B is spaced andparallel to the center line 46A of the oval opening 20 of the frame 16D,and so on. By so locating the frames 16, a tip 50 of the frame 16D nearthe notch 22B thereof can be located between tips 52 and 55 of theframes 16A and 16B, respectively.

By locating the tip 50 between the tips 52 and 55, the center points ofthe oval openings of the frames 16A, 16B, and 16D can be located closerto one another. This can be accomplished even though each frame 16 has arelatively long length L2. The frames 16 are then located over a smallerarea than would for example be possible in a rectangular array.

Each mirror 18 has an approximate oval shape with a length L3 and awidth W3. The length L3 is typically about 300 microns and the width W3about 250 microns.

Each mirror 18 is located within a respective oval opening 20 with itslength L3 along the length L1 of the oval opening 20 and its width W3along the width W1 of the oval opening 20. Each mirror 18 is secured toa respective frame 16 with two mirror torsion components 54. Each mirrortorsion component 54 has first and second opposed ends 56 and 58respectively. The first end 56 is non-rotationally secured to the mirror18.

The mirror torsion component 54 extends from the first end 56 into arespective one of the notches 22A or 22B. The second end 58 of themirror torsion component 54 is non-rotationally secured to the frame 16within the notch 22A or 22B. The mirror 18 is thereby suspended withinthe oval opening 20 of the frame 16. A center point of the mirror 18coincides with a center point of the oval opening 20. There is a minimumspacing M as measured from a surface of the mirror 18 to a surface ofthe oval opening 20 directly next to the notch 22A. Although the minimumspacing M is relatively small, the mirror torsion component 54 isrelatively long due to the depth of the notch 22A while stillmaintaining strength of the frame 16.

The mirror can pivot relative to the frame 16 about the center line 46,whereupon each mirror torsion component 54 winds up, or twists against atorsion spring force thereof. The entire length of the mirror torsioncomponent from the first end 56 to the second end 58 winds up, ortwists. The length of each mirror torsion component 54 allows it to havea higher torsion spring constant with a corresponding smaller forcebeing applied to rotate the mirror 18 by a certain degree.

Electrostatic terminals 64 are formed on the substrate 12. Theelectrostatic terminals 64 are used to pivot the frame 16 or the mirror18 by electrostatic attraction. The support structure 14 also serves asan electrostatic barrier between electrostatic terminals and adjacentmirrors 18. The apparatus 10 may be used in an optical switch wherein arespective circular bundle of light shines from a respective opticalfiber onto a respective one of the mirrors 18. The light may shine in adirection 66 which is at an angle 68 of, for example, 45° with respectto a plane in which the substrate 12 extends. A usable portion of thebundle of light falls between the width W3 of the mirror 18. The bundleof light is usually circular in cross section so that it typically has ausable length which equals its usable width. Because of its length L3 ofthe mirror 18, the entire usable length of the bundle of light falls onthe mirror 18. The oval shape of the mirror 18 thereby allows for theentire usable width and length of the bundle of light to be reflectedtherefrom, even though the light shines in the direction 66 and evenwhen the frame 16 is pivoted as shown in FIG. 2 so that the mirror 18 ispivoted with respect to the frame 16. It should be noted that the ovalshape of each mirror 18 also makes more efficient use of space than forexample a rectangular mirror, thereby allowing for the mirrors 18 andframes 16 to be located over a smaller area.

Mirrors 18 are thus used which have lengths L3 which are longer thantheir widths W3. In addition, relatively long mirror torsion components54 and frame torsion components 56 are used. Regardless of thedimensions of the mirrors 18 and the torsion components 54 and 26, themirrors 18 are still located relatively close to one another. Therelatively close positioning of the mirrors 18 is due to a combined useof a honeycomb support structure 14 which also serves as anelectrostatic barrier, the notches 22A, 22B, 24A, 24B, the oval shapesof the mirrors 18 together with closely matching shapes of the ovalopenings 20, and the arrangement of the frames 16 in a non-rectangulararray wherein a tip 50 can be located between the tips 52 and 54. Bylocating the mirrors closer to one another a smaller array is formed. Asmaller array results in a smaller optical switch and a reduction inpath length that light has to travel before reaching and after beingreflected by a mirror. A reduction in path length of the light reduceslosses in quality and intensity of light.

In the foregoing specification, the invention has been described withreference to specific exemplary embodiments thereof. It will, however,be evident that various modifications and changes may be made theretowithout departing from the broader spirit and scope of the invention asset forth in the appended claims. The specification and drawings are,accordingly, to be regarded in an illustrative rather that a restrictivesense.

What is claimed is:
 1. A micromachined apparatus for reflecting light,comprising: a support structure; and a plurality of mirrors each beingpivotally secured to the support structure, a first to a third adjacentones of the mirrors being located at comers of a first triangle, eachcorner being less than 90°.
 2. An apparatus according to claim 1 whereinthe mirrors are located at corners of a plurality of contiguoustriangles, each triangle having three corners, each of which is lessthan 90°.
 3. An apparatus according to claim 1 further comprising aplurality of support frames, each support frame being pivotally securedto the support structure, the first, second and third mirrors beingsecured to a first, second, and third of the support frames,respectively.
 4. An apparatus according to claim 3 wherein the thirdsupport frame is partially located between the first and second supportframes.
 5. An apparatus according to claim 4 wherein a respective mirrorpivots relative to a respective support frame about a respective mirrorpivot axis, the mirror pivot axis about which the third mirror pivotsbeing located between the mirror pivot axes about which the first andsecond mirrors pivot.
 6. An apparatus according to claim 1 furthercomprising an electrostatic barrier structure located between the firstand second, the first and third, and the second and third mirrors.